This invention relates to methods and apparatus for connecting together leads of rotors, and more particularly to connection of an axial lead to a riser lead in a revolving magnetic field of a water-cooled turbogenerator.
In rotors of rotary electric machines of a large size, particularly of turbogenerators, an increase in the capacity of a rotor makes it necessary to cause a cooling liquid of high thermal capacity, such as water or oil, to flow through the field coils in order that cooling can be carried out effectively. In such case, a cooling liquid is supplied from one end of a rotor shaft to flow therethrough in a manner such that the cooling liquid will flow through hollow leads in the rotor shaft to the field coils arranged in the vicinity of the outer marginal portion of a rotor drum. The cooling liquid which has done work is discharged from one end of the rotor shaft. Thus there is a need to provide a radially oriented liquid passage for connecting each hollow lead to each field coil. The present practice is to use a lead pipe for this purpose. Thus the lead pipe performs a dual function of passing a cooling liquid therethrough and conducting an exciting current to the field coils.
The hollow lead should be connected or joined to the lead pipe in a manner such that there will be no leakage of the cooling medium through the joint, a current can be conducted satisfactorily and the joint has high mechanical strength. However, in a turbogenerator which rotates at high speed, difficulty is encountered in forming a satisfactory joint between the hollow lead and the lead pipe due to a small space available because of the need to reduce the diameter of the rotor and the difficulty with which insulation is effected.